Day Eleven - Summing Amplifier and Difference (Differential) Amplifier - 4/6/17

Hello, today we continued our topic on op-amp. We revisited some materials on inverting and non-inverting amplifiers and talked more on other types of amplifier, for examples, unity buffer, summing, and difference amplifier.

Note that both inverting and non-inverting amplifier only depend on the external resistance.

Top is for inverting. Bottom is for non-inverting.

For unity buffer amplifier, the purpose of this amplifier is to keep the voltage constant while increasing the output current.

For summing amplifier, which is a variation of inverting amplifier, the purpose of this amplifier is to perform summation of input voltages.

For difference amplifier, the purpose of this amplifier is to perform subtraction of input voltages.

LAB - Summing Amplifier

Design:

Since we need Vout = Va + Vb, R1 must be equal to R3 in order to get Vout = -(Va+Vb).

The actual resistance for R1,R2,R3 we used are 6.73k, 6.67k, and 6.71k ohms. 

Result: 

Using the V- as -5V, V+ as +5V, 1V for one of the input and varying another input voltage, we measured the output voltage as:

Comparing the calculated and measured values of the output voltages, we have exactly almost the same result. Note that the only inaccurate result is found at the output voltage exceeded the saturation voltage. At that point of output voltage, the result is not reliable because the voltage has met the maximum or minimum output. We only consider the linear part for the operation. 

LAB - Difference Amplifier

Design:

Differential Amplifier is also called as a difference amplifier because it receives both the voltage inputs from positive terminal and negative terminal, then find the difference of the input voltages.

Result:
The actual resistance values we used are R1 = 9.94k, R2 = 19.9k, R3 = 9.98k, R4 = 19.7k ohms resistors.

Using Vb = 1V, V+ = +5v, V- = -5v , and varying Va, we get the output voltages as above.

From the graph above, we get the similar curve that we get from previous labs.

The curve can be divided into three parts.

Positive saturation part, linear part, and Negative saturation part.

Comparing the measured values to the calculated values, we found that this data set has relatively more error because the saturation is small, and the output voltage can easily be bigger or smaller than the VCC.

Summary:
We saw that op-amp is a important device for electrical engineering because of their variations on its operations. Summing and Difference amplifiers are the basic op-amp which not only perform the basic mathematical operation but also enable the existences of digital-to-analog converter and instrumentation amplifier. But there is a point to remember, "Always remember they will saturate at some point".